1. Field of the Invention
The present invention relates to a liquid heating apparatus and an image forming apparatus.
2. Description of the Related Art
As an image forming apparatus including a printer, a fax machine, a copy machine, a plotter, a multifunction peripheral with combined functions thereof, and the like, an inkjet recording apparatus, for example, that uses a liquid ejection recording method, in which a recording head is used for ejecting an ink droplet, is known. In the image forming apparatus using the liquid ejection recording method, image forming (“recording”, “printing”, etc., are used as synonyms of “image forming”) is performed by ejecting an ink droplet from a recording head onto a conveyed sheet. There are a serial type image forming apparatus and a line type image forming apparatus. In the serial type image forming apparatus, an image is formed by having droplets ejected while the recording head is moving in a main-scanning direction, and in the line type image forming apparatus, an image is formed by having droplets ejected while the recording head is stationary.
It should be noted that, in the present application, “image forming apparatus” refers to an apparatus in which image forming is performed by ejecting ink onto a medium such as a paper medium, a string medium, a fiber medium, a towel medium, a leather medium, a metal medium, a plastic medium, a glass medium, a wood medium, a ceramic medium, etc., (including a simple liquid ejection apparatus). Further, “image forming” means not only that a meaningful image such as a character or a figure is being attached to the medium but also that a meaningless image such as a pattern is being attached to the medium (droplets are simply being ejected onto the medium). Further, “ink” is not limited to something referred to as ink, but may be used as a generic term for any kind of liquid that can be used to form images such as those referred to as recording liquid, fixing processing solution, liquid. Further, “sheet” is not limited to materials such as paper, but includes an overhead projector (OHP) sheet or a cloth, or materials on which ink droplets can be attached, and may be used as a generic term for things referred to as a recording medium, a recording paper, or a recording sheet, etc.
As a liquid ejection head (liquid droplet ejection head) used for a recording head, piezoelectric heads and thermal heads are known. In piezoelectric heads, a volume of a liquid chamber is changed by a moving diaphragm moved by a piezoelectric actuator, pressure in the liquid chamber is increased, and thus, liquid droplets are ejected. In thermal heads, the pressure in the liquid chamber is increased by bubbles generated by heat of a heating element, and thus, liquid droplets are ejected.
In the image forming apparatuses of a liquid ejection method as described above, there is a kind of ink that has high viscosity at room temperature. When an ink with high viscosity is used, in many cases, the ink is heated in order to reduce the viscosity in advance before the ink is supplied to an inkjet head through a supply tube. A technique is known in which preliminary heating is provided for the ink by disposing a liquid heating apparatus (preliminary heating apparatus) in the middle of an ink supply path from an ink tank to the inkjet head.
As an image forming apparatus with this kind of liquid heating apparatus, conventionally, image forming apparatuses described in Patent Documents 1 and 2 are known. The image forming apparatus described in Patent Document 1 includes a recording head for ejecting ink, an ink tank for storing the ink, and a flexible supply tube disposed in between the ink tank and the recording head.
The above supply tube includes an internal tube which forms a first flow path in which supplied ink flows from the ink tank to the recording head, and an external tube which is disposed around the internal tube. A second flow path is formed between the internal tube and the external tube. In the second flow path, temperature control liquid flows in order to control temperature of the ink flowing in the first flow path.
In contrast, a liquid ejecting apparatus described in Patent Document 2 includes a recording head for ejecting ink onto a sheet and an ink heating apparatus that is connected to the recording head via an ink flow path and is capable of adjusting temperature. The ink flow path is provided in order to allow the ink to flow from an upstream ink cartridge to a downstream recording head, and to supply the ink to the recording head. The ink flow path is arranged in such a way that it goes through a housing space that houses the recording head.